SPECIES OF PASTURE GRASSES

SINCE about 1850, when trade increased with the outside world, plant introductions of many sorts began to make vast changes in the native vegetation. Clearings of land for cultivated crops, forest fires, and grazing aided in its destruction.

One of the characteristics of an isolated insular vegetation is that existing plant associations are easily upset by exotic species. And, except for the forest reserves and land in the higher elevations where the native vegetation has been subjected to the least disturbance, Hawaii is a land of exotic species; the grazing industry depends almost solely on them.

Not all introductions, whether deliberate or accidental, have been desirable; some have become serious pests because the natural vegetation cannot hold them in check. But the result has been the gradual development of a varied series of desirable pasture swards, each adapted to its particular climatic zone. The Hawaii Agricultural Experiment Station, established in 1901, and other Government institutions and private agencies have made thousands of introductions from all parts of the world. The station maintains a series of testing plots at varying altitudes to determine the value and specific zonal adaptability of each species.

Many of the better known forage species have been introduced into Hawaii, but all the possibilities have by no means been exhausted. Forage plant exploration in the Tropics is essentially a virgin field; even the more advanced parts of the Tropics have not completely evaluated the forage possibilities of the species occurring there. Few concerted attempts have been made through selection and breeding to improve the species in common use. Since most tropical forage crops are perennial and are commonly propagated vegetatively, there has been little attempt to purify them.

Our experience has been that seed introductions from various sources, especially those in which the plant is endemic, segregate into greatly varied forms. These in themselves, or through hybridization, should make possible advances in greater production or development of strains for specific uses or qualities.

The Hawaiian rancher, because of the diversity of climates and soil types, especially if his ranch extends over several vegetation zones, has to vary his methods of developing, using, and managing his pastures and the species he plants. In the nonarable range lands, he depends primarily on the natural forage and employs only the cheapest methods of establishing more desirable species. His improved paddocks, however, call for careful consideration of what species to plant.

First to consider, of course, is adaptability, which in the ecological sense means the ability of the plant to persist in a given zone under the environmental conditions existing in the pasture.

Species for Grazing

Dallisgrass is one of the most important of tropical grazing species in Hawaii. It is adapted to a wide range of conditions throughout zones C and D from sea level to 6,000 feet. It will stand hard and continuous grazing and has a high carrying capacity. Some pastures carry as much as one animal to an acre throughout the year. It has the further advantage that other species of grasses and legumes will grow in association with it, especially if the sod is plowed every 5 years or so.

Kikuyugrass is the most maligned and the most praised of grasses. Its proponents point to its advantages of ease and speed of establishment, its ability to hold many pasture pests like guava partly in check, the protection it gives against soil erosion, its wide adaptability, its high carrying capacity and ability to withstand heavy and continuous grazing, and its apparently satisfactory nutritive value as measured by beef gains. Its opponents object primarily to the very characteristic that gives it virtue it tends to sweep everything before it, good and bad, and become a one-species pasture. Probably its greatest value is in zone D, where its quick ground coverage and ability to hold pests in check are important.

Paragrass has value in the poorly drained, heavy soils of the coastal flats and river valleys of zone D. It grows fairly well at elevations up to 2,000 feet. It will not persist under heavy, continuous grazing, but with rotational grazing and on fertile soils and ample moisture it has a high carrying capacity. It is not extensively used for grazing beef cattle.

Molassesgrass is not liked at first by animals, but many ranchers consider it an acceptable forage. An advantage is that seed of excellent quality can be purchased. The seedlings develop rapidly into a semibunchgrass, often 3 feet high; the trailing stems tend to grow over taller shrubs. It seeds in the fall, and in the dryer zones it regenerates itself by natural seeding. Grazing experiments at the Haleakala Branch Station on Maui, 2,200 feet elevation, indicate that it cannot withstand excessive trampling or hard continuous grazing, but it will maintain itself indefinitely either as clumps or, when there is sufficient rainfall, as closely cropped crowns.

Napiergrass, generally regarded as a cut forage crop, is used in intensively managed grazing paddocks. An experiment at the Haleakala Farm has shown it to have a yearly carrying capacity of 1 1/2 animals an acre. Our practice has been to fertilize it with at least 450 pounds of ammonium sulfate a year, applied in two or three applications. Napier succumbs if it is grazed continuously; a desirable practice is to graze 40 to 50 percent of the time, by using enough animals to consume all the leaves in about 2 months and allowing about 2 months of rest. Normally, the animals eat only the green leaves and the succulent top part of the stem. During the resting period, nodal buds develop a fine leafy growth on these stems. New basal shoots replace them mostly during the spring months. Mowing or disking down these productive stems reduces the carrying capacity. If it is necessary to mow or disk in order to destroy volunteer pests, it is best to do it in the early spring just before the major development of basal shoots.